Abstract

715,331. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 20, 1952 [Aug. 7, 1951], No. 18624/51. Class 40 (3). [Also in Group XL(c)] In a television receiver automatic gain control (A.G.C.) is obtained by clamping the black level at a pre-determined value and deriving an A.G.C. potential dependent upon the amplitude of the synchronizing pulses in the clamped signal. The composite demodulated signal is applied over an amplifier to the grid E of the picture-tube, via a blocking condenser C1. The black level is stabilized at earth potential by means of diodes D1, 2, which are biased to be non-conductive save during the " back-porch " period, the gating means comprising negative-going pulses derived from a winding L1 on the line output transformer. The gating pulses are suitably delayed by means of a time-delay network comprising inductance L2, condensers C2, 3 and terminating resistances R5, 6. The A.G.C. potential is derived in accordance with the synch. signal amplitude by means of a peak-rectifying diode D3, part only of the D.C. output being utilized by means of a potentiometer R7, 8. In an alternative embodiment, Fig. 2 (not shown) in which the picture tube is cathode modulated, the black level is stabilized at the grid of the video amplifier and the A.G.C. potential derived at this point.

GB1862451A1951-08-071951-08-07Improvements in or relating to television receivers
ExpiredGB715331A
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